There are several well tools, such as plugging devices, for use in oil and/or gas wells, having a housing with a through bore, a frangible disc provided in the through bore and a breaking mechanism provided in the housing for breaking the frangible disc. In the initial state, the frangible disc will prevent fluid flow through the bore. After the frangible disk has been broken, fluid flow through the bore is allowed.
In the oil industry it is known that different types of plugging devices are used during pressure testing of petroleum wells, for example, before start-up of production from the well, or when extensive maintenance of the well has been carried out. A plugging device will then be installed in the well, after which an area of the well will be pressurised, so as to check that pipe joints, packers, valves etc. are properly installed, and whether they are also leak-tight. The plugging device is usually installed as a lower part of production tubing, the plugging device then being arranged in a pipe element that is designed to be connected with one or more pipe elements forming the production tubing. The plug may also be arranged in an independent pipe element which will then be capable of being run down inside a liner or a casing, the liner or casing being installed in the well beforehand.
Once the pressure testing has been completed and production is to start up, the plugging device must be removed from the well, either by the plugging device being retrieved or by the whole or parts of the plugging device being destroyed downhole.
Such plugging devices comprise an outer housing, in which outer housing is arranged one or more elements that will prevent a fluid flow across the plugging device.
Plugging devices that are to be retrieved from the well may be connected to a wire (wireline) or the like, whereby the wire is used to retrieve the plugging device. Such plugging devices might, however, become wedged during retrieval or, in particular if downhole for a long time, they might have reacted with the tubing in which, for example, they are arranged, and so become stuck, which means the plugging devices are difficult or even impossible to bring up to the surface again.
For the above reasons, so-called destructible plugging devices have been developed, where the plugging device remains in the well, but where parts of the plugging device are destroyed such that a fluid flow is permitted across the plugging device. Such destructible plugging devices are made of one or more materials that will dissolve when the material/materials come into contact with a liquid, for example, a chemical or water. For instance, such a plugging device may be made of a rubber material, this rubber material being brought into contact with the well fluid or the chemical once testing of the well has been carried out, so as to dissolve the rubber material.
However, during operations from floating rigs, this method will be far too unreliable and slow, seen in the light of the operating costs for such a platform. In this case, it will not be possible to predict the exact time at which the plugging device is removed and passage through the well opens.
Such destructible plugging devices can also be made of a material that can be broken up or crushed by using explosives or mechanical loading devices, where this material, for example, may be of glass, ceramics or the like. Use of explosives will provide a sure removal of the plugging device, but will be a safety risk, and there are also many countries that have stringent requirements regarding the use and import of explosives. Mechanical loading devices are often highly complex and thus prone to faults.
Such tools are for example known from NO 20130427, NO 20110630, NO 20081192, all of which are owned by Vosstech AS.
The disadvantage of the prior art tools are that the breaking mechanisms are relatively complex and/or not possible to predict the time at which the plugging device is removed, with the result that their operation may be unreliable. Hence, one or more embodiments of the present invention may provide a tool with a more reliable breaking mechanism.
An actuation tool is often required. First, a bailing operation is performed in order to remove debris, mud etc. above the tool to provide access to a connection interface of the tool, then the actuation tool is connected to the connection interface of the tool and finally the actuation tool is used to actuate the breaking mechanism to break the frangible disk, Hence, one or more embodiments of the present invention may provide a tool where the bailing operation can be omitted or simplified.
WO 2010/120774 A1 describes a bridge plug arrangement with a plug made of a frangible material which may be broken into a plurality of pieces. The plug has an opening in which a mandrel is connected by means of nuts. It is shown that the plug can be disintegrated by applying a force to the mandrel by means of a jar. There are several disadvantages with this type of solution. First of all, there is contact between the nuts and plug, which, when glass is used as a plug material, increases the risk for unintentional disintegration of the glass during topside handling of the arrangement and during insertion into the well. In order to reduce the risk of such unintentional disintegration of the glass, the contact area between glass/nuts should be large. However, a large contact surface area will make it difficult to disintegrate the plug intentionally again by forcing the nut into the glass.
NO 331150 B1 describes a device for removal of a plug which is used in a well, a pipe, or the like for carrying out tests. An element is arranged to penetrate into the plug material so that this is crushed, said element is arranged to be supplied said force from an above lying element. The element is preferably a ring, the lower end of which is arranged to be forced in a radial direction into the plug element at axial driving of a hydraulic pressure piston.
GB 2437657 describes a well isolation device having an axial passage in fluid communication above and below the device. A frangible barrier seals the passage to block fluid flow through the passage and thereby bears a load from fluid pressure. A structural element acts on the frangible barrier to selectively redirect the load on the frangible barrier element, thereby preventing or facilitating rupture. The structural element may be a disengagable constraint formed by a movable sleeve that forms a compression-loaded structure when in contact with the frangible barrier. Upon disengagement, the frangible barrier bears a primarily tensile load that facilitates its rupture. The frangible barrier may be hemispherical.
Magnum Oil Tools is marketing a plugging device called “Dual MagnumDisk” (http://www.magnumoiltools.com/dual-magnumdisk) comprising two half-spherical ceramic discs used as a pressure barrier. A product video (http://www.youtube.com/watch?v=mVTH62opPzc, at ca 1:58) discloses a spear submerged down into the well, breaking the ceramic discs by applying a stroke onto the discs. The disadvantage here is, as mentioned above, that debris, sand, mud etc will obstruct the well above the discs, making it impossible to achieve contact between the spear and the discs. Hence, a bailing operation will be necessary.
One or more embodiments of the present invention may provide a plugging device that will provide a safe and reliable destruction of the plugging device.